We discuss fire as part of environmental and human health. Our process-based, comprehensive, and quantitative approach encompasses combustion and heat transfer, and fire effects on people, plants, soils, and animals in forest, grassland, and woodland ecosystems from around the Earth. Case studies and examples link fundamental concepts to local, landscape, and global fire implications, including social-ecological systems. Globally, fire science and integrated fire management have made major strides in the last few decades. Society faces numerous fire-related challenges, including the increasing occurrence of large fires that threaten people and property, smoke that poses a health hazard, and lengthening fire seasons worldwide. Fires are useful to suppress fires, conserve wildlife and habitat, enhance livesk grazing, manage fuels, and in ecological restoration. Understanding fire science is critical to forecasting the implication of global change for fires and their effects. Increasing the positive effects of fire (fuels reduction, enhanced habitat for many plants and animals, ecosystem services increased) while reducing the negative impacts of fires (loss of human lives, smoke and carbon emissions that threaten health, etc.) is part of making fires good servants rather than bad masters.